Seyed Amir Arsalan ShamsJae Wung BaeJae Nam KimHyoung Seop Kim...
115-128页
查看更多>>摘要：In this study,the deformation behaviors and related microstructural evolutions were investigated in ei-ther monotonic or cyclic deformation modes in an interstitial metastable high-entropy alloy.These inves-tigations aimed to reveal the mechanisms underlying the superior low-cycle fatigue(LCF)life of this alloy.A thermomechanical process was applied to induce fine-grained(FG)and coarse-grained(CG)microstruc-tures in Fe-30Mn-10Co-1OCr-0.4C(atomic percentage)alloy.Their superior combination of strength and ductility was attributed to the appearance of deformation-induced ε-martensite and the presence of car-bon.The CG alloy showed a greater volume fraction of ε-martensite than the FG alloy in the monotonic deformation mode,and vice versa in the cyclic mode.Such a disparity was interpreted in light of the back-stress effect of the relaxed y-grain boundaries in the latter mode.Meanwhile,the γ-to-ε phase transformation under cyclic loading at low strain amplitudes(0.4％)barely led to an improved fatigue life as compared with that at higher strain amplitudes(≥0.55％).The high reversibility of partial disloca-tion motions under cyclic loading and delaying the formation of dislocation cells through the martensitic transformation could explain why the alloys investigated in this study exhibited a superior LCF life com-pared with high-entropy alloys reported in previous studies.
查看更多>>摘要：A(ZrC/SiC)3 alternate coating was deposited on sharp leading edge(SLE)C/C composites by chemical va-por deposition(CVD).The ablation behavior was examined via oxyacetylene torch with heat flux of 2.38 MW/m2.The results indicated that the alternate coating exhibited great ablation resistance,providing an effective protection for C/C composites.In initial rapid heating stage,the(ZrC/SiC)3 alternate coating can relieve thermal stress,avoiding the peeling of coating and keeping an intact coating structure.In subse-quent ablation,the SiC layers in central region were consumed rapidly,leaving layered interspaces.Three stacked ZrO2 layers were reserved with the assistance of the release of thermal stress by interspaces,offering a great anti-scouring effect.In transition and border regions,the alternate SiC layers can delay oxygen erosion of inner coating and C/C substrate by the formation of SiO2.It is believed that the results would be helpful for the design and application of anti-ablation coatings on SLE C/C composites.
查看更多>>摘要：The commercialization of the lithium-sulfur(Li-S)batteries is severely hampered by the shuttle effect and sluggish kinetics of lithium polysulfides(LiPSs).In this study,porous tubular graphitic carbon ni-tride(PTCN)was synthesized as the sulfur host by hydrothermal treatment,thermal shock and etching methods.By etching technology,the hollow nanotube tentacles grow on the tube wall of PTCN,the meso-porous appears on the inner wall,and a large number of nitrogen defects are introduced.The vertically-rooted hollow nanotube tentacles on the PTCN surface facilitate electron conduction for sulfur redox reactions.The hollow and porous architecture exposes plentiful active interfaces for accelerated redox conversion of polysulfide.Furthermore,the nitrogen defects in PTCN enable more excellent intrinsic con-ductivity,higher adsorbability and conversion catalytic activity to LiPSs.Based on the above synergetic effect,the batteries with PTCN/S cathodes realize a high discharge capacity of 504 mAh g-1 at 4 C and a stable cycling behavior over 500 cycles with a low capacity decay of 0.063％per cycle.The results indicate a promising approach todesigning a high performance electrode material for Li-S batteries.
查看更多>>摘要：MXenes,a family of two-dimensional(2D)materials,exhibit peculiar microwave-absorbing behaviors due to their unique chemical composition and structure.Although laminated Ti3C2Tx MXenes with a multi-layer structure have been used for microwave absorption,real 2D MXenes with a single-layer structure have not yet been investigated.Here,the electromagnetic wave response behavior of single-layer Ti3C2Tx MXenes was explored in detail.The permittivity of Ti3C2Tx MXene rises dramatically with an increase in filler loading,and Ti3C2Tx MXene features a distinct dielectric response wherein dipolar polarization and interfacial polarization makes a greater contribution at low filler loading;conductive loss becomes more prominent at high filler loading.Versus laminated Ti3C2Tx MXene,single-layer Ti3C2Tx MXene delivers superior absorbing capability:The RLmin value of SL-Ti3C2Tx-22％reaches-43.5 dB at 6.5 GHz,and a broad EAB of 6.88 GHz can be attained at a thickness of 1.8 mm due to enhanced dipolar polarization,interfacial polarization,and conductive loss.This work is of great significance in guiding the future development of MXene-based absorbers.
查看更多>>摘要：Metallic sodium(Na)is believed to be a promising anode material for sodium-ion batteries(SIBs)due to its low electrochemical potential,high theoretical specific capacity,superior electrical conductivity,and so on.However,issues such as high chemical activity,the growth of Na dendrites,large volume change,and unstable interface impede its practical application.We design a cheap iron(Fe)-based substrate dec-orated by a thin liquid metal Ga layer for stable and dendrite-free Na metal anodes in low-cost carbonate electrolytes.The inherent mechanism of Ga-based liquid metal in inhibiting the growth of Na dendrites was revealed for the first time.Liquid metal Ga with sodiophilic property can act as nucleation seeds to decrease the nucleation barrier and induce homogeneous Na+flux,resulting in uniform and dendrite-free Na deposition.Full cells with Na3V2(PO4)3 cathode were also assembled to verify the practical application ability of the modified Na metal anode.Under the regulation of the liquid metal layer,the Coulombic ef-ficiency,cycling life,and capacity of batteries are obviously enhanced.The strategy proposed here cannot only reduce the cost of batteries but also improve their electrochemical and safety performance.
查看更多>>摘要：Annealing is one of the most efficient heat treatment to refine the grain microstructure in metal alloys.Prior to the annealing,an aging treatment can be implemented to precipitate the second phases for more nucleation sites in deformed mixed grains during subsequent recrystallization.However,the underlying mechanism behind the second phases and recrystallization has not yet been fully understood.Taking a typical deformed nickel(Ni)-based(GH4169)superalloy as an exapmle,this research aims to clairfy the connections between the recrystallization and delta(δ)phase(Ni3Nb)during annealing.All deformed samples were also treated by aging and then annealing.The results show that the microstructure and component of δ phase dominated the recrystallization nucleation in the Ni-based alloy.Moreover,there was the presence of the δ phase interval limiting nucleation(PILN)and δ phase protecting nucleation(PPN),when a high content of close-set phase was precipitated from the matrix.The PILN determined the primary condition for the recrystallization nucleation that happended at the interval of 8 phase larger than the critical nucleation size.The peak nucleation occurred in the PPN,where the recrystallization nucleus were free of the penetration by the adjacent grains,before the nucleation incubation time was reached.Thus,a new feasible JN theory was proposed to determine the maximum domain of recrystal-lization nucleation under close-set precipitated phases.All the possible nucleation sites were assumed under PPN in the JN theory.As such,the original microstructure can be expected to design for the an-nealing via the aging process.A quantitative evaluation of recrystallization nucleation can also achieved in the Ni-based alloys during aging.
Hyo Ju BaeKwang Kyu KoMuhammad IshtiaqJung Gi Kim...
177-188页
查看更多>>摘要：Assessing the stacking fault forming probability(Psf)and stacking fault energy(SFE)in medium-or high-Mn base structural materials can anticipate and elucidate the microstructural evolution before and after deformation.Typically,these two parameters have been determined from theoretical calculations and empirical results.However,the estimation of SFE values in Fe-Mn-C ternary systems is a longstanding debate due to the complicated nature of carbon:that is,whether the carbon doping indeed plays an important role in the formation of stacking faults;and how the amount of carbon atoms exist at grain boundaries or at internal grains with respect to the nominal carbon doping contents.Herein,the use of atom probe tomography and transmission electron microscopy(TEM)unveils the influence of carbon-doping contents on the structural properties of dual-phase Fe-17Mn-xC(x=0-1.56 at％)steels,such as carbon segregation free energy at grain boundaries,carbon concentration in grain interior,interplanar D-spacings,and mean width of intrinsic stacking faults,which are essential for SFE estimation.We next determined the Psf values by two different methods,viz.,reciprocal-space electron diffraction measure-ments and stacking fault width measurements in real-space TEM images.Then,SFEs in the Fe-17Mn-xC systems were calculated on the basis of the generally-known SFE equations.We found that the high amount of carbon doping gives rise to the increased SFE from 8.6 to 13.5 mJ/m2 with non-linear varia-tion.This SFE trend varies inversely with the mean width of localized stacking faults,which pass through both other stacking faults and pre-existing s-martensite plates without much difficulty at their intersect-ing zones.The high amount of carbon doping acts twofold,through increasing the segregation free energy(due to more carbon at grain boundaries)and large lattice expansion(due to increased soluble carbon at internal grains).The experimental data obtained here strengthens the composition-dependent SFE maps for predicting the deformation structure and mechanical response of other carbon-doped high-Mn alloy compositions.
查看更多>>摘要：Although the antimony(Sb)has been widely used to modify potassium sodium niobate(KNN)ceramics for tailoring the phase structure and performance,the role of Sb still remains insufficiently understood,consequently hindering the understanding of the physical origin of high-performance KNN-based ceram-ics.Here,we combine the experiments and first-principles calculations to deeply reveal the effects of Sb on KNN ceramics.Our results reveal a re-entrant-like relaxation behavior near the rhombohedral-orthorhombic(R-O)phase transition at the low content of Sb,which transforms into a canonical one at higher content of Sb.First-principles calculations show a significantly decreased difference in the bond length of six B-O bonds of NbO6 octahedral in Sb-modified KNN ceramics compared to pristine KNN ceramics,responsible for the low-temperature re-entrant-like dielectric relaxation.Furthermore,the ad-dition of Sb would soften the B-O repulsion and gradually break the long-range ferroelectric ordering,resulting in the occurrence of nanoscale domains and enhanced local heterogeneity.Finally,we find that the optimized piezoelectric properties are the trade-off between the long-range ferroelectric ordering and the local heterogeneity.Therefore,this work not only deeply reveals the effects of Sb on KNN ceramics from multi-scale perspectives but also helps the future composition design for achieving high piezoelec-tricity.
查看更多>>摘要：Improving the separation efficiency of photogenerated carriers and broadening the light absorption range of the photocatalyst are two important factors for improving the performance of the photocatalyst.In this paper,a new and efficient Z-scheme CdS/iron phthalocyanine(CdS/FePc)core-shell nanostructure composite material is prepared by a simple solid-phase reaction method.There are two key points in the preparation of composite materials:one is that hydrogen bonding energy is closely connected with FePc,another is that FePc can be uniformly assembled on CdS nanoparticles.The photocatalytic hydrogen evolution(PHE)of the CdS/FePc nanocomposite(73.01 μmol/h)is 2.6 times higher than that of pure CdS(26.67 μmol/h).In addition,after 4 photocatalytic cycles,the PHE of the CdS/FePc composite is still 92.3％of the first cycle.There are three reasons for this situation:(1)The Z-scheme heterojunction is formed to improve the separation efficiency of photogenerated carriers;(2)FePc expands the visible light absorp-tion range of CdS;(3)The large core-shell contact area is favorable for the separation of photo-induced carriers at the interfaces.This research is conducive to the further development of new photocatalytic materials with high efficiency,low cost and simple preparation.
查看更多>>摘要：Photocatalysis is considered as one of the most promising technologies to generate renewable energy and degrade environmental pollutants.Tremendous efforts have been made to improve photocatalytic efficiency.Among these,tuning spin polarization and introducing an external magnetic field are con-sidered two promising strategies to boost photocatalytic performance.Herein this review highlights the recent breakthroughs through manipulating spin states and applying external magnetic fields for enhanc-ing photocatalytic reactions.The relevant characterization techniques and fundamental mechanisms are summarized.Spin polarization states of photocatalysts have received considerable attention due to their unique roles,including inhibiting the recombination of photoexcited carriers owing to spin orientation constraint,enhancing the reaction product selectivity,and reducing the reaction barriers via optimizing the absorption energy and binding strength.As for the effects of external magnetic field on photocatalytic performance,we mainly discuss the separation enhancement of photoinduced carriers under static and time-varying magnetic fields and the magneto-hydrodynamic effect of charged particles.Lastly,the nega-tive magnetoresistance effect is discussed due to the synergistic effects of the electron spin state and an external magnetic field.These discussions in this review may provide new insights into designing new semiconductors for boosting photocatalytic performance in internal and external magnetic fields.
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